The present invention relates to a gas pipe line leakage detecting method and apparatus for detecting gas leaks in a gas pipe line.
While various leak detecting methods have been proposed in the past for use with liquid transmission pipe lines, there exist the following considerable differences between the liquid transmission pipe line and the gas pipe line and therefore the hitherto proposed leak detecting methods for liquid transmission pipe lines cannot be applied as such to the gas pipe line.
Firstly, gas is a compressible fluid and therefore the line packing quantity of the gas within the pipe line is subject to dynamic variations. Thus, there occur the following phenomena which are not encountered in the liquid pipe line. For instance, a considerable time is required before the effect of a change in the pressure, flow rate or the like at one end appears at the other end. Moreover, the effect reaches in a considerably weakened form at the other end due to the attenuation and diffusion of the effect during its propagation through the pipe line. Of course, it is impossible to produce synchronization between the two events and also the effect does not simply appear at the other end with a given time delay.
Next, a change in the pressure, flow rate or the like due to the occurrence of a leak is much smaller than in the case of a liquid and the attenuation is also so large that it is extremely difficult to distinguish the change from various variations which always occur during the ordinary operation. Also, the propagation time of the change is extremely slow as compared with that of the liquid.
In view of these facts, the detection of a gas leak has been effected by the following methods.
The conventional methods have been mainly of the type which effects the detection of a gas leak by the use of a gas detector including a sensor to directly sense a leaked gas component, and it has been the usual practice that the gas detector is arranged at a place having a high probability of a leaked gas. In the case of a yard, the gas detector is mounted within the valve house; in the case of a gas pipe line a patrol car equipped with the gas detector makes the round for monitoring purposes. Also, a report has been made of a method in which a sound generated at a leak site by a leakage gas is picked up by a portable microphone.
From the operation standpoint of a gas pipe line, the usual practice is such that the pressure is measured at the dispatching base, destination base or midway point of the pipe line and compared with its predetermined upper and lower limit values, thereby indirectly determining the occurrence of a leak upon detection of an abnormal condition, and generally only the detection of large leakage is possible. Also, the predetermined values are frequently dependent on the personal experience of the operator himself and they are not universal, thus frequently tending to cause an error.
Further, all of the conventional methods are disadvantageous in that they are capable of effecting only a localized monitoring and they are incapable of continuously monitoring the gas pipe line over its whole extent.